rosenfe

in my 79 5 speed can i use regular?

wpgshark

Pros
8.5 compression, I would think detonation wouldn't be an issue.

Cons
No knock sensor so nothing to compensate for detonation.

James Bailey

it runs best on regular....was designed for it !

Tomkat80222

Way to many people use higher octane gas thinking it will improve performance and other things. But the reality is that this is not the case. Here at altitude we use a lower octane gas (85 and in the mountains 83) so that it burn more quickly. The high octane helps the gas burn more slowly and not explode your engine apart in high compression sea level environments.

mark kibort

i use regular in the BMW and Chevy tahoe with NO downside or pinging.
i only use premium in the race car, but its 11:1 and most with my engine use a mix of 100 and 92 octane.
there is a little more power potential in reglular if you can use it without it pinging, and in the older cars, thats not an issue, so dont waste money

928 DesMoines

I use 91 Octane here in Des Moines. It is the only fuel here that doesn't have ethanol in it. Avoid the alcohol.

ROG100

IIRC all 4.5L USA/CAN & ROW used regular
4.7L onwards was super.

Fogey1

Almost six years ago Andrew Olson did a great service for the 928 community by scanning and posting the Owner's Manuals for many years and model variations.
Owner's Manual - Online
https://rennlist.com/forums/928-foru...al-online.html

The Owner's Manual for my 1983 US 928S (4.7L) discusses fuel in several places. While I hate to disagree with Roger, these quotes are useful in addressing the octane question:

On Page 97:
Fuel recommendation
91 RON (87 CLC on U.S. fuel pumps) minimum. UNLEADED FUEL ONLY. Fuel tank capacity: 23 U.S. gals, or 86 liters.

On Page 63, there's a discussion of what the octane numbers mean on US pumps:
Octane ratings
Octane rating indicates a gasoline's ability to resist detonation. Therefore, buying the correct octane gas is important to prevent engine damage.

Regular fuels have an octane rating ranging from 91 to 95 RON (Research Octane Number), which corresponds to 87 to 91 CLC (U.S. Cost of Living Council octane rating).

The 91 RON octane rating which you will find on a label on the right side of the engine compartment of your car is based on the research method. The CLC octane rating usually displayed on U.S. gasoline pumps is calculated as research octane number plus motor octane number, divided by 2, that is:

RON + MON
2

The CLC octane rating is usually 4 points lower than the RON rating:
91 RON equals 87 CLC
95 RON equals 91 CLC

I note the Euro 83S, with its higher compression (10-1 vs 9.3-1), requires higher octane fuel according to its owners manual.
http://928gt.com/t-928engine.aspx

I also note the factory was not a fan of gasohol, see page 64.

oldfrat

It was designed for 87 octane. Try to keep it as full as possible when storing it.

Brad

ROG100

Fogey1 - no worries as I was going from memory which these days is spotty.

So the information gleaned from the Owners Manuals would suggest that ----

4.5L cars both ROW & USA/CAN 77 to 82 used Regular gas
4.7L USA/CAN 83 to 84 cars used Regular

All the rest used Super - maybe some Country Specific differences here and there.

Don Carter

I have only been burning mid-grade in all my 928s, but this thread was a good reminder, I could be burning regular in the 82. I haven't noticed any pinging with the S4s, but they have knock sensors, so I guess they should never ping, but I may not be getting full power. The 86.5 has Ken's chips designed for mid grade.

Also, if you are choosing between mid grade and premium for your 4.7+ car, it's more than just an octane choice. With Shell gas, you do get more additives in the V-Power premium fuel, so if you really want to keep your valves and injectors as clean as possible, go with premium. (I'm too cheap and don't get an employee discount :-) )

Petza914

Here's a twist, what about forced induction in an 4.5L (supercharger). Still lower compression ratio, but additional load and stress, and no knock sensor, correct? Is it safest to run Premium in this case or is mid-grade 89 OK, or even 87?

What's the consensus? Thanks.

mark kibort

low compression ratio without boost... as soon as you have any boost, that ratio goes up proportionally. if you do the math for CR, and you have 7lbs of boost..... do the math again for compression ratio and take 1.5 x the stroke and see what you get!
generally in all boosted cars, you want to run premium or greater, depending on the boost level

Petza914

Thanks Mark. I've been running 93 Premium, but wanted to verify that's what I should be doing, which I'll continue to.

Imo000

I've been running regular in my '85 32V before it was boosted and occasionally when I had to use it for daily driving because the DD car was down for repairs BUT I made sure to stay out of boost regardless of the temptation. You can do I've a boosted car with regular just as long as you staybout of boost AND you remember what is in the tank before you roll on the throttle.